In the past electrochemical detector techniques have been widely used for on-line voltammetry and low resolution liquid chromatography. However despite the rapid advances that have been made in the column technology of high pressure liquid chromatography, a serious limitation to development and use of this method has been the lack of a suitable detector system. High pressure liquid chromatography involves the resolution of substances which are only present in the eluting solution in trace amounts. The requirements of an electrochemical technique to detect such trace eluents are (1) high sensitivity (2) detectors with ultra-low cell volume (3) a wide range of response (4) large linear range of operation (5) little influence of experimental parameters, e.g. temperature, flow rate etc. and (6) long term stability and reliability.